/*
 * Copyright (c) 2010, 2020 Oracle and/or its affiliates. All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.glassfish.grizzly.http.server.util;

/**
 * Utility class for string parsing that is higher performance than StringParser for simple delimited text cases.
 * Parsing is performed by setting the string, and then using the <code>findXxxx()</code> and <code>skipXxxx()</code>
 * families of methods to remember significant offsets. To retrieve the parsed substrings, call the
 * <code>extract()</code> method with the appropriate saved offset values.
 *
 * @author Craig R. McClanahan
 * @version $Revision: 1.3 $ $Date: 2007/06/18 14:17:08 $
 */

public final class StringParser {

    // ----------------------------------------------------------- Constructors

    /**
     * Construct a string parser with no preset string to be parsed.
     */
    public StringParser() {

        this(null);

    }

    /**
     * Construct a string parser that is initialized to parse the specified string.
     *
     * @param string The string to be parsed
     */
    public StringParser(String string) {

        super();
        setString(string);

    }

    // ----------------------------------------------------- Instance Variables

    /**
     * The characters of the current string, as a character array. Stored when the string is first specified to speed up
     * access to characters being compared during parsing.
     */
    private char chars[] = null;

    /**
     * The zero-relative index of the current point at which we are positioned within the string being parsed.
     * <strong>NOTE</strong>: the value of this index can be one larger than the index of the last character of the string
     * (i.e. equal to the string length) if you parse off the end of the string. This value is useful for extracting
     * substrings that include the end of the string.
     */
    private int index = 0;

    /**
     * The length of the String we are currently parsing. Stored when the string is first specified to avoid repeated
     * recalculations.
     */
    private int length = 0;

    /**
     * The String we are currently parsing.
     */
    private String string = null;

    // ------------------------------------------------------------- Properties

    /**
     * Return the zero-relative index of our current parsing position within the string being parsed.
     */
    public int getIndex() {

        return this.index;

    }

    /**
     * Return the length of the string we are parsing.
     */
    public int getLength() {

        return this.length;

    }

    /**
     * Return the String we are currently parsing.
     */
    public String getString() {

        return this.string;

    }

    /**
     * Set the String we are currently parsing. The parser state is also reset to begin at the start of this string.
     *
     * @param string The string to be parsed.
     */
    public void setString(String string) {

        this.string = string;
        if (string != null) {
            this.length = string.length();
            chars = this.string.toCharArray();
        } else {
            this.length = 0;
            chars = new char[0];
        }
        reset();

    }

    // --------------------------------------------------------- Public Methods

    /**
     * Advance the current parsing position by one, if we are not already past the end of the string.
     */
    public void advance() {

        if (index < length) {
            index++;
        }

    }

    /**
     * Extract and return a substring that starts at the specified position, and extends to the end of the string being
     * parsed. If this is not possible, a zero-length string is returned.
     *
     * @param start Starting index, zero relative, inclusive
     */
    public String extract(int start) {

        if (start < 0 || start >= length) {
            return "";
        } else {
            return string.substring(start);
        }

    }

    /**
     * Extract and return a substring that starts at the specified position, and ends at the character before the specified
     * position. If this is not possible, a zero-length string is returned.
     *
     * @param start Starting index, zero relative, inclusive
     * @param end Ending index, zero relative, exclusive
     */
    public String extract(int start, int end) {

        if (start < 0 || start >= end || end > length) {
            return "";
        } else {
            return string.substring(start, end);
        }

    }

    /**
     * Return the index of the next occurrence of the specified character, or the index of the character after the last
     * position of the string if no more occurrences of this character are found. The current parsing position is updated to
     * the returned value.
     *
     * @param ch Character to be found
     */
    public int findChar(char ch) {

        while (index < length && ch != chars[index]) {
            index++;
        }
        return index;

    }

    /**
     * Return the index of the next occurrence of a non-whitespace character, or the index of the character after the last
     * position of the string if no more non-whitespace characters are found. The current parsing position is updated to the
     * returned value.
     */
    public int findText() {

        while (index < length && isWhite(chars[index])) {
            index++;
        }
        return index;

    }

    /**
     * Return the index of the next occurrence of a whitespace character, or the index of the character after the last
     * position of the string if no more whitespace characters are found. The current parsing position is updated to the
     * returned value.
     */
    public int findWhite() {

        while (index < length && !isWhite(chars[index])) {
            index++;
        }
        return index;

    }

    /**
     * Reset the current state of the parser to the beginning of the current string being parsed.
     */
    public void reset() {

        index = 0;

    }

    /**
     * Advance the current parsing position while it is pointing at the specified character, or until it moves past the end
     * of the string. Return the final value.
     *
     * @param ch Character to be skipped
     */
    public int skipChar(char ch) {

        while (index < length && ch == chars[index]) {
            index++;
        }
        return index;

    }

    /**
     * Advance the current parsing position while it is pointing at a non-whitespace character, or until it moves past the
     * end of the string. Return the final value.
     */
    public int skipText() {

        while (index < length && !isWhite(chars[index])) {
            index++;
        }
        return index;

    }

    /**
     * Advance the current parsing position while it is pointing at a whitespace character, or until it moves past the end
     * of the string. Return the final value.
     */
    public int skipWhite() {

        while (index < length && isWhite(chars[index])) {
            index++;
        }
        return index;

    }

    // ------------------------------------------------------ Protected Methods

    /**
     * Is the specified character considered to be whitespace?
     *
     * @param ch Character to be checked
     */
    protected boolean isWhite(char ch) {

        if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n') {
            return true;
        } else {
            return false;
        }

    }

}
